For example, with a mechanism using an air cylinder to lift or lower a lifting table on which a workpiece is loaded, as described above, a constant air pressure is supplied to the air cylinder, however, in order to maintain the lifting or lowering speed of the lifting table constant, the air pressure supplied to the air cylinder must be constantly changed. But, since there had existed a difference between such required air pressure, i.e., an air pressure to be constantly varied, and the supplied constant air pressure, the lifting or lowering speed of the lifting table had been incapable of being maintained constant, thereby various inconveniences had been caused.
Then, in order to avoid such inconveniences, there has been proposed a cylinder pressure adjusting unit which allows the lifting or lowering speed of a lifting table, or the like, to be maintained substantially constant by adjusting the fluid pressure supplied to a cylinder through a regulator (Patent Document 1: Japanese Patent No. 4729359).
The cylinder pressure adjusting unit is a cylinder pressure adjusting unit which adjusts the fluid pressure supplied to a cylinder by means of a regulator, being provided with a pressure switching means between the rod of the cylinder and the regulator to allow the setting pressure for the regulator to be freely switched in accordance with the advance/retraction motion of the cylinder rod. The pressure switching means includes an adjusting spring which is provided in the regulator, being expanded or contracted to thereby switch the setting pressure to the cylinder, and a connection member comprised of a rack and a spur gear engaged therewith for expanding or contracting the adjusting spring.
However, this cylinder pressure adjusting unit presents problems that it has a number of component parts, providing a complex and large construction; especially that the rod of the air cylinder for initial pressure setting is largely protruded, thereby a space covering the protrusion being required; and that it is difficult to steplessly change the cylinder pressure for lifting or lowering the workpiece at a desired speed, or rapidly positioning the workpiece to stop it at a desired position.